Pen



FIG. 1 is an upper front perspective view of a pen showing my new design;

FIG. 2 is a front elevation view thereof, with the rear, right side, and left side elevation views being a mirror image of the front elevation view;

FIG. 3 is an enlarged top plan view thereof; and,

FIG. 4 is an enlarged bottom plan view thereof.

The broken lines shown in FIG. 4 illustrate environmental subject matter and form no part of the claimed design. 

CLAIM The ornamental design for a pen, as shown and described. 